1. Field of the Invention
The present invention relates to an object velocity measuring apparatus and an object velocity measuring method. More particularly, this invention relates to an object velocity measuring apparatus and an object velocity measuring method which extract an object from a video image and measure the two-dimensional moving velocity of the object in the photographic field. The velocity in the photographic field may be called the angular velocity. The image is photographed with an imaging device.
2. Description of the Related Art
This type of apparatus is applied to a surveillance camera, an object tracking apparatus, and the like. The parameters characterizing an object include the moving velocity of the video image (hereinafter, referred to as the object velocity) on the screen. A first known approach of measuring the object velocity is to subject the image to a motion vector process, such as block matching, thereby measuring the object velocity from the image. A second known approach is to measure a change in the object position coordinates for each frame, while correlating the object positions between a plurality of successive image frames and calculate the object velocity from the measured value.
With the first approach, however, when the size of the object in the image is small, it is difficult to sense the area where the object moves. Furthermore, since the first approach is based on block matching, the velocity measuring accuracy is limited to blocks (that is, pixels) at best.
On the other hand, since the surroundings of the imaging device vary severely outdoors, the signal component of the object in the image decreases or the noise component increases, which can prevent the object from being sensed temporarily. In this case, it is difficult to correlate the object positions between the frames. Moreover, parts of the object area extracted from the image can be separated from or connected to one another on a frame basis. In this case, it is difficult to correlate segments between a plurality of frames. Under such circumstances, the second approach is particularly unsuitable for measuring the object velocity outdoors.
As described above, since the existing approaches have a limit to the object velocity sensing accuracy, an approach capable of measuring the object velocity with still higher accuracy has been desired. Furthermore, in a state where the surroundings vary seriously, the object velocity sometimes cannot be sensed. Therefore, there has been a need to provide a approach of measuring the velocity in a robust manner.